Adopt pyzfs from ClusterHQ

This commit introduces several changes:

• Update LICENSE and project information
• Give a good PEP8 talk to existing Python source code
• Add RPM/DEB packaging for pyzfs
• Fix some outstanding issues with the existing pyzfs code caused by changes in the ABI since the last time the code was updated
• Integrate pyzfs Python unittest with the ZFS Test Suite
• Add missing libzfs_core functions: lzc_change_key, lzc_channel_program, lzc_channel_program_nosync, lzc_load_key, lzc_receive_one, lzc_receive_resumable, lzc_receive_with_cmdprops, lzc_receive_with_header, lzc_reopen, lzc_send_resume, lzc_sync, lzc_unload_key, lzc_remap

Note: this commit slightly changes zfs_ioc_unload_key() ABI. This allow
to differentiate the case where we tried to unload a key on a
non-existing dataset (ENOENT) from the situation where a dataset has
no key loaded: this is consistent with the "change" case where trying
to zfs_ioc_change_key() from a dataset with no key results in EACCES.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: loli10K <ezomori.nozomu@gmail.com>
Closes #7230